Figure 4

Integrins apicalise early during CB polarisation. During CB migration, Integrins (βPS1 immunolabel) are predominantly located on the advancing apical edge (A, arrow), with low levels on the basal trailing edge (arrowhead). Integrin is not detected on lateral CB surfaces, yet at the same stage, Robo is detected on apical, lateral and basal membrane domains (B). Dystroglycan is excluded from lateral cell surfaces, and is concentrated at both apical and basal membranes (C). At stage 17, migration is complete, and the heart lumen is formed. The apical and basal distribution of Integrin has not changed (D), however, Robo (E) and Dystroglycan (E) are now almost entirely apical. Apicalisation of Integrin is reduced in robo, lea mutants at stage 15 (G) and 17 (H). The inset in (G) shows the intensity of immuno-labeling at the same gain as the other βPS1 panels. Dystroglycan apicalisation is similarly affected in robo, lea mutants (I). The asterisks in stage 15 panels identifies βPS1 label in the amnioserosa. Arrows mark apical surfaces, and arrowheads mark basal surfaces of the CBs. Calibration: 10 microns